1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing chips for a thixomolding-process injection molding machine, and more particularly to novel improvements for manufacturing a high-purity raw material for recycling by charging into a chip manufacturing device primary crushed pieces obtained by fragmenting and crushing wastes occurring during the molding of a metal alloy and wastes of metal alloy products, and by processing them into chips whose surfaces are polished and in which impurities are removed.
2. Related Art
Conventionally, in a process for molding a magnesium alloy, for example, a die-casting process is generally adopted in which a melt of 620 to 700.degree. C. which is completely melted in a melting furnace is cast into a mold at high pressure.
In contrast, the thixomolding process is a molding process in which a chip-like raw material of a metal alloy is charged into a hopper, and the chips are heated above a solidifying point and below a melting point inside a cylinder by a heater, are thus set in a semimolten state in which the liquid phase and the solid phase coexist, and are poured into a mold.
This injection molding process excels over the die-casting process in the following points:
(1) A melting furnace is not required for the plant.
(2) A large-scale fire-prevention measure is not required for the plant.
(3) A covering flux is not required.
(4) Treatment of dross and sludge is not required.
(5) Melting skills and experience are not required.
(6) The energy cost can be reduced.
(7) Since the raw material with a grain size of 1 to 8 mm is used, there is no possibility of the chips being ignited.
(8) The dendrite (a crystal with a treelike branching pattern) is crushed by a screw and is formed into fine particles with diameters of 35 to 75 mm, and the fluidity of the semimolten metal increases, so that moldings with thin wall thicknesses can be formed.
(9) A completely molten metal whose viscosity is low is liable to form a turbulent flow, but the flow of a semimolten metal whose viscosity is high becomes closer to a laminar flow, so that the amount of a gas entrained is small, and bubbles are therefore difficult to be formed in moldings.
(10) Since the semimolten metal solidifies faster than the completely molten metal, it is possible to reduce the molding cycle time.
(11) The life of the mold can be extended.
(12) The dimensional accuracy improves.
(13) The working environment is excellent.
Partly due to a move toward enactment of a "Household Electrical Appliance Recycling Law," Japanese and foreign major consumer electrical appliance manufacturers, automobile manufacturers, and injection molding manufacturers have en bloc shifted to magnesium alloy moldings that are 100% recyclable and are produced by injection molding which is superior to the die-casting process.
In addition, the magnesium alloys have such characteristics as a heat radiating characteristic and an electromagnetic-wave shielding characteristic in addition to its light weight, thin size, and high rigidity, and is capable of expressing a higher-quality feature than an alloy resin body. Thus, the magnesium alloys have outstanding characteristics.
On the other hand, in the conventional regeneration of magnesium alloy scraps, the scraps are remelted and refined to form ingots, and the ingots were formed into chips again so as to be used.
Although recycling is 100% possible according to the above-described conventional method, a large amount of energy is required, and countermeasures against pollution and waste treatment, including the treatment of exhaust gases, dross, and sludge, are required, resulting in high cost.